1. Field of the Invention
This invention relates generally to the accurate measuring of the fluid flow rate in pipes and conduits, and more particularly to the flow in gravity sewer systems. The apparatus is portable and lightweight, and can be used to measure the flow rate in a buried pipeline without requiring the operator to enter the manhole. The device can easily be inserted into a flowing pipe well below street grade, and flow measurements can be taken quickly. Carefully calibrated weir/orifice plates allow measurement of a wide range of flows during both free flow through the apparatus, when the weir/orifice plate acts as a weir, and low-pressure flow through the apparatus, when the weir/orifice plate acts as an orifice, as well as in the transitional zone therebetween.
2. Description of the Prior Art
Heretofore, relevant art has taught flow measuring devices that require the temporary installation of a weir or flume together with a device which detects the liquid depth upstream of the weir or flume and then converts the depth to rate of flow. Such an installation requires individuals to enter the manhole and invest considerable time and labor in positioning the metering device, diverting the flow into the device and calibrating the liquid depth measuring device. Previous weir or flume devices are limited in their flow range because in high-flow conditions they become submerged and lose their flow measuring characteristics. An assembly containing an integral weir/orifice which can measure both free-flow conditions and surcharged conditions, as well as conditions in the transitional zone, and which is portable, easily installed from ground level and quickly sealed in the flow path upon insertion into the subject pipe or conduit, is highly desirable. However, although the need for such a device has been apparent for a considerable time, no such device has been forthcoming until now.